The level of assaults in prisons in the last three months was the highest ever recorded.
Photograph: Graeme Robertson for the Guardian

Prison suicides and the level of assaults in jails were at an all-time high in the last year, figures show.

The latest safety in custody statistics confirm an increase in violence and despair in prisons which the new justice secretary, Liz Truss, conceded was unacceptable.

They showed there were 105 “self-inflicted deaths”, which include suicides and accidental deaths as a result of the person’s own actions, in the 12 months to June 2016, 23 higher than the previous 12 months, representing an increase of 28%. In the second quarter of 2016 alone there were 31 self-inflicted deaths, the highest ever level in a single quarter.

The number of self-inflicted deaths by women increased from one in the previous 12 months to 11. This suggests more than one in 10 prison suicides were by women, at a time when women make up fewer than one in 20 of the prison population.

Overall the rate of self-inflicted deaths has increased from 1 per 1,000 prisoners to 1.2 per 1,000. And death rates generally increased to 321 – a rise of 30%.

The figures also revealed that incidents of self-harm were up 27% to 34,586. But the number of murders in prisons decreased from seven in the previous year to five.

Separate performance results named six prisons in England and Wales whose overall performance was deemed to be of serious concern. They were Bristol, Doncaster, Hewell, Isis, Liverpool and Wormwood Scrubs.

Truss said she was “determined to make sure our prisons are safe and places of rehabilitation”.

She added: “The level of violence in our prisons is unacceptable. I am clear that safety in prisons is fundamental to the proper functioning of our justice system and a vital part of our reform plans.

“There are a number of factors including the availability of psychoactive substances in prisons which must be tackled. It will take time to address these long-standing problems.”

Andrew Neilson, director of campaigns at the Howard League, said: “Prisons are not only becoming more dangerous; they are becoming more dangerous more quickly.

“That more prisons have been awarded the worst-possible performance rating provides further indication of how the system is failing after years of rising numbers, chronic overcrowding and deep staff cuts.”

Neilson added: “It is particularly shocking to see a dramatic increase in the number of women taking their own lives. In the past, a sharp rise in the number of women dying in prison has prompted a government review and promises of action. The high levels of violence and deaths should shame us all, and the new secretary of state for justice and her ministers must set out concrete plans to reduce them.”

Mark Day, head of policy at the Prison Reform Trust, said: “These shocking figures show where the justice secretary must begin on prison reform. Making prisons safe for everyone who lives and works in them is the absolute priority and the necessary bedrock for longer term change.”

The Labour MP Karen Buck, a member of the human rights committee, said the figures pointed to a crisis in prisons brought on by overcrowding and cuts in staff.

She said: “These latest prison statistics paint a horrifying picture. Conditions in many of our prisons seem to be deteriorating at alarming speed, whether measured in terms of staff safety, assaults on prisoners or self-harm. Prisons should be safe places for detention and rehabilitation, not of danger.”

Karen Buck (@KarenPBuckMP)

Crisis in our prisons not surprising given over-crowding and cuts in prison staff. Was this not wholly foreseeable? https://t.co/6iARknVoMC